1. Field of the Invention
The invention relates to the field of electrical buses particularly where a plurality of transmitters transmit onto a common bus.
2. Prior Art
Often, many transmitters and receivers are connected to a common electrical path or bus. Various control mechanisms are used to regulate transmission to prevent two transmitters from transmitting simultaneously. For instance, in Ethernet, collisions between signals are detected and retransmission occurs at random times. In other systems, a "token" is passed between the transmitters to enable one transmitter at a time. Arbitration circuits are used in still other systems to permit transmission to occur on a priority basis or in the order requested. Countless other mechanisms are used to prevent interference on a bus.
In investigating transmission difficulties over a common bus used on a computerized branch exchange, a peculiar bus interference was discovered which resulted in the present invention. This interference is of the type that resembles simultaneous transmission by two transmitters. However, in the branch exchange, the expanders which are equivalent of the transmitters, each have unique addresses, and address signals are transmitted from a common source preventing simultaneous transmission. The nature of this interference will be described in detail in conjunction with FIG. 1.